This invention relates to furnaces and boilers and more specifically relates to furnaces and boilers utilizing impervious, low permeability silicon carbide as a medium for efficiently absorbing infrared radiation.
In processes for heating and vaporizing liquids and gases there are many types of boilers or furnaces that perform specific functions within a well-defined set of parameters such as upper heat limits and pressure levels. All boilers are either directly or indirectly energized by chemical or fossil fuels which may be in the form of liquids, gases or solids. All of these boilers generate pollution and, with the exception of nuclear boilers, are limited to relatively low heat levels and pressure limits. Further, these prior art boilers have been characterized as having a less than optimum efficiency.
Furthermore, in many processes ranging from the debarking of logs in the production of pulp paper and firing furnaces for steel mills to the burning of fuels for internal combustion engines, substantial quantities of waste heat are generated which are never fully utilized. To make use of the emission of waste heat many types of heat exchangers have been developed, an example of which is disclosed in Cushman U.S. Pat. No. 3,404,731. These prior art heat exchangers have a primary purpose of capturing heat from a waste heat source, conducting that heat to a liquid or gas medium which transfers the latent heat absorbed in the exchanger process to another medium. To make such a waste heat exchanger desirable for an end use, the exchanger must have a second medium which can efficiently utilize and convert the waste heat to a useful end.
It is known that carbonaceous materials provide good heat absorption properties and the use of carbonaceous materials in furnaces is well known in the art. For example, in Reys U.S. Pat. No. 3,265,124 there is disclosed a furnace having a plurality of heat exchanger tubes therein which are coated with a graphite material to improve the efficiency of the furnace. Other furnace arrangements have utilized graphite material to cover portions of the surface thereof in order to provide increased heat transfer efficiently.
As is known in the art, carbon materials are typically porous and accordingly have a high premeability. In addition, such carbon and graphite materials are typically pervious so that any furnace utilizing such carbon or graphite materials requires an impervious backing or support structure to provide the necessary strength to withstand pressures developed within the furnace or boiler. More recently, high impervious carbonaceous materials have been developed which exhibit low permeability characteristics. An example of one such material is "KT" silicon carbide manufactured by the Carborundum Corporation, which material has exceedingly high strength characteristics and can operate at temperatures as high as 3000.degree. F in an oxidizing atmosphere and 4200.degree. F in an inert atmosphere. Further, this material is impermeable having a porosity of 0% with an excellent thermal shock resistance characteristic.
It is an object of this invention to provide a carbonaceous boiler or furnace formed of a low permeability, impervious carbonaceous material capable of efficiently converting infrared radiation to heat a gas or liquid material.
It is another object of this invention to provide a carbonaceous boiler/heat exchanger for converting infrared radiation and the heat of waste combustion products to heat a fluid.
It is yet another object of this invention to provide a boiler formed of carbonaceous material which is capable of converting the infrared radiation from natural sunlight and from an artifical source to heat a gas or liquid.
It is yet another object of this invention to provide a carbonaceous boiler formed of a low permeability, impervious carbonaceous material capable of heating and vaporizing liquids and gases in both relatively normal temperature ranges and in superheat and superpressure ranges.
It is yet another object of this invention to provide a carbonaceous boiler formed of a low permeability, impervious carbonaceous material capable of efficiently converting nuclear radiation to heat a gas or liquid material.
It is yet another object of this invention to provide a carbonaceous boiler formed of a low permeability, impervious carbonaceous material capable of utilizing vapor or gas of fuels that produce superheat flames, e.g. hydrogen and acetylene.
It is yet another object of this invention to provide a boiler formed of a carbonaceous material which is capable of heating and vaporizing liquids and gases to the plasma state.
It is yet another object of this invention to provide a boiler formed of a carbonaceous material which is capable of being washed, scrubbed, or scaled without disassembling.
It is another object of this invention to provide a carbonaceous boiler formed of a low permeability, impervious carbonaceous material capable of vaporizing acids, bases, or salts.